Curly top virus in California: review, current management practices and future directions
2015
Rivara, C. J.
Beet curly top virus (BCTV) belongs to the family Geminiviridae, genus Curtovirus. The virus is vectored by the beet leafhopper Circulifer tenellus. With a wide host range BCTV overwinters in western foothills proximal to the extensive southern Central Valley growing region. It is well adapted to the wet winter/dry summer climate of central California. In the spring, beet leafhopper typically migrates from the drying foothills to the irrigated valley, vectoring the virus to a variety of crops. With the exception of very late infections, crop loss is immediate and permanent across all susceptible crop hosts. In the fall beet leafhopper returns to the foothills to overwinter and reproduce, repeating the cycle. Dependent on wildlands, annual insect populations and virus titer vary considerably between years. Agriculture in California has a long history of major BCTV outbreaks, starting in 1919 affecting sugar beet, and to a lesser extent melons and beans. In 1943 the California Department of Food and Agriculture initiated a disease management program focused on control of overwintering leafhoppers. The Curly Top Virus Control Program (CTVCP) performs seasonal monitoring of leafhopper development and concentration with the objective of controlling late instar nymphs with insecticide treatments prior to dispersal to the valley. BCTV seldom impacted California processing tomatoes before the mid-1960s as California tomato production centered in northern and coastal valleys plus direct seeded production with high plant populations minimized the stand loss characteristics of the disease. Since the mid-1990s, the shift to low populations of transplants has greatly increased the risk for loss from BCTV. In the spring of 2013, leafhopper populations were exceptionally high due to adequate fall rains to establish specific leafhopper hosts, coupled with little spring rainfall to limit competing non-host grasses. Large leafhopper populations and abundant virus presence and environmental restrictions on specific sites resulted in unprecedented damage. Losses from the epiphytotic in 2013 is estimated to have cost about one million short tons of fruit. That loss has renewed industry interest in exploring diverse management topics including resistance breeding, direct seeding of critical areas, insecticides, row covers, and repellants. The State program is pursuing expanded vector control, polymerase chain reaction (PCR) detection of infected leafhoppers and hosts, and improving risk communication.
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